i) Field of the Invention
The present invention relates to a process for producing optically active .gamma.-hydroxyketones which can be used as intermediates for preparing optically active tetrahydrofurans useful as optically active moiety in biodegradable polymers, perfumes, intermediates for synthesizing medicines and the like.
ii) Description of the Background Art
Since optically active .gamma.-hydroxyketones can be converted into their corresponding optically active tetrahydrofurans, which are useful as optically active moiety in various compounds, by subjecting them to intramolecular acetalation, they are important as industrial raw materials.
The following two processes have already been known as processes for synthesizing such optically active .gamma.-hydroxyketones.
(i) A process in which an optically active .gamma.-diol is oxidized to obtain its corresponding optically active .gamma.-hydroxyketone. PA1 (ii) A process in which nickel chemically modified is used as a catalyst to asymmetrically hydrogenate a .gamma.-diketone, thereby synthesizing its corresponding optically active .gamma.-hydroxyketone.
More specifically, in J. Chem. Soc. Perkin Trans., 2148-2154 (1977), (2R,5R)-2,5-hexanediol is oxidized in the presence of silver carbonate-Celite to obtain (R)-5-hydroxyhexane-2-one in a yield of 46%.
More specifically, in Bull. Soc. Chem. Belg., 100, 585-595 (1991), 2,5-hexanedione is used to subject it to asymmetric reduction, thereby obtaining (R)-5-hydroxyhexane-2-one in a yield of 78.7% (optical purity: 10.1% ee).
In the process (i), the optically active .gamma.-diol is used as a starting material. The processes for synthesizing this optically active .gamma.-diol were reported in J. Org. Chem. 54, 1755-1756 (1989); Tetrahedron Asymmetry, 7(2), 569 (1991); Tetrahedron Lett. 28(50), 6335-6338 (1987); and Tetrahedron Asymmetry, 3(3), 333-336 (1992). All these processes suffer from such problems that the reaction process takes a long period of time, the yield of the product is poor, and the optical purity of the product is low. On the other hand, the process (ii) can not be used industrially because the optical purity of the product is too low.